Laser diode device

ABSTRACT

A laser diode device has a housing with a mounting part and a laser diode chip, which is based on a nitride compound semi-conductor material, in the housing on the mounting part. The laser diode chip is mounted directly on the mounting part by means of a solder layer and the solder layer has a thickness of greater than or equal to 3 μm.

This patent application is a national phase filing under section 371 ofPCT/EP2013/054890, filed Mar. 11, 2013, which claims the priority ofGerman patent application 10 2012 103 160.6, filed Apr. 12, 2012, eachof which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

A laser diode device is specified.

BACKGROUND

Light sources having a high optical power density are key components fora multiplicity of applications. By way of example, laser diodes composedof a nitride-based compound semiconductor material system have a highmarket potential for projection systems, in particular those havingluminous fluxes of between 1000 and 20,000 lumens.

Therefore, components having high output powers and compact housings arerequired for such applications. For cost reasons and in the context ofstandardization, housings of the so-called TO type series (TO:“transistor outline”) in the form of TO metal housings (“TO metal can”)are customary, for instance in the form of the known structural sizesTO38, TO56 and TO90, wherein the TO metal housings are substantiallymanufactured from steel. Such standard TO designs, also designatedhereinafter as “TO housings” for short, are usually used nowadays forlaser diodes. However, currently available laser diodes in TO housingshave been limited heretofore to optical powers of less than 3 watts,which is insufficient for many applications. To date, however, it hasnot yet been possible to achieve optical powers of above 3 watts withsuch designs.

By way of example, the document C. Vierheilig et al., Proc. SPIE, vol.8277, 82770K, 2012 discloses blue-emitting nitride-based laser diodes inTO housings which, at room temperature in continuous wave operation, canemit light having a wavelength in the range of 440 nm to 460 nm with anoutput power of a maximum of 2.5 watts.

In the case of such laser diodes, the TO housings have thermalinadequacies, in particular during mounting, which is customary fortechnical reasons, with that side of the substrate which faces away fromthe semiconductor layer sequence on a heat sink between a housing and alaser diode, such that the semiconductor layer sequence is arranged atthe top as seen from the housing (“Epi up”).

Alongside the standard TO housings composed of high-grade steel, TOhousings are also known which, for better heat dissipation, have a basethat is based on copper or has a copper core and a steel surface.However, studies have been able to show that the use of such modified TOhousings alone does not lead to an increase in the output power of laserdiodes.

In the case of red and infrared power laser diodes, in particular on thebasis of arsenides, thermally optimized mounting concepts with verydirect heat dissipation are known, in particular mounting with that sideof the semiconductor layer sequence which is situated opposite thesubstrate downward (“Epi down”) on a heat sink between the laser diodeand a housing and furthermore the use of a copper carrier instead of aTO housing.

Such measures are unsuitable for nitride-based laser diodes, however,since a cost-effective capping for protecting the laser againstcontamination and mechanical damage is not possible for a coppercarrier. Particularly moisture and chemicals, for example, in the caseof use in the automotive sector, can be critical and necessitate ahermetic capping in order to protect the laser diodes from such externalinfluences. Since, in the case of nitride-based laser diodes, the p-sideis typically arranged on that side of the active region which faces awayfrom the substrate, and is made as thin as possible, since the operatingvoltage can increase with increasing thickness of a p-dopednitride-based semiconductor layer, “Epi down” mounting in turn, owing tothe active region thus situated very near the p-type contact in the caseof nitride-based laser diodes, during the soldering process, forexample, can easily lead to short circuits and thus to a reduction ofthe yield.

SUMMARY OF THE INVENTION

Specific embodiments specify a laser diode device.

In accordance with at least one embodiment, a laser diode devicecomprises a housing, in which a laser diode chip is arranged on themounting part by means of a solder layer.

The housing can preferably be mountable with an outer area on anexternal heat sink, for example, a cooling body or a printed circuitboard. At least the mounting part and preferably all regions of thehousing which are situated between the laser diode chip and the outerarea which is provided for mounting the laser diode device on such anexternal heat sink comprise a material having a high thermalconductivity, for example, a metal, for example, preferably copper orelse aluminum, or a ceramic material, for example, AlN. Furthermore, atleast the mounting part can also comprise a composite material and canbe formed, for example, by a metal-core circuit board having a metallayer enveloped by a plastic material. Furthermore, the mounting part,for making electrical contact with the laser diode chip, can have anelectrical lead, for example, in the form of a conductor track, and asoldering area. If the mounting part is formed by a main body composedof metal on the side facing the laser diode chip, the electrical leadcan be made possible by the main body itself.

In accordance with a further embodiment, the housing has a housingcover, which is applied above the mounting part and closes the housing.The housing cover furthermore has a window, through which the lightemitted by the laser diode chip during operation can be emitted from thelaser diode device. The housing cover can comprise, for example, a metalsuch as, for instance, steel, in particular high-grade steel, or else aceramic material or be composed thereof, apart from the window.Particularly preferably, a hermetically impermeable closure of thehousing can be made possible by the housing cover. By way of example,the housing cover can be welded to the mounting part or a furtherhousing part.

In accordance with a further embodiment, the housing has a housing partconnected to the mounting part. The mounting part can extend away fromthe housing part along an extension direction. In other words, themounting part can project away from the housing part and can be embodiedin a pin-type fashion, for example. In this case, the mounting partpreferably has a mounting area, which extends away from the housing partalong the extension direction of the mounting part and on which thelaser diode chip is arranged.

The housing part can be provided and designed, in particular, for makingit possible to arrange a housing cover for closing the housing on thehousing part. The housing part and the mounting part, which, inparticular, can also be embodied integrally with one another, preferablyeach have a main body composed of copper or else, in the case ofintegral embodiment, a common main body composed of copper. As analternative thereto, the main body can also comprise some other materialfrom among those mentioned above.

At least the housing part can furthermore be steel-sheathed. That meansthat the housing part is substantially formed from the main body and iscovered with a steel layer. The steel layer can be formed, for example,by a layer composed of high-grade steel. A steel sheathing of thehousing part can be particularly advantageous since it is therebypossible, as in the case of a standard TO housing having a steel base,for a housing cover to be welded to the housing part. In this case, themounting part projects into the housing cover from the housing partalong its extension direction, such that the laser diode chip, with thehousing cover mounted, is situated on the mounting part in the cavityformed by the housing cover and the housing part.

In accordance with a further embodiment, in addition to the housingpart, the mounting part is also steel-sheathed. In particular, thehousing part and the mounting part in this embodiment can have a commoncopper main body covered with a steel layer.

Particularly preferably, the housing can be embodied as a so-called TOhousing, for example, having a structural size TO38, TO56 or TO90. Inthis embodiment, the housing part can also be designated as “base plate”and the mounting part as “stem”. In comparison with standard TO housingswhich are usually used and which have at least one housing part or ahousing part and a mounting part which substantially consist of steeland do not have a copper-based main body, the housing in this embodimenthas a higher thermal conductivity on account of the copper of thesteel-sheathed housing part.

In accordance with a further embodiment, the mounting part or else, ifappropriate, a housing part can have holes or openings, for example,through which electrical leads, for example, in the form of contactlegs, can project from that side of the housing which faces away fromthe mounting part to the side on which the mounting part is arranged.The electrical leads can be provided for making electrical contact withthe laser diode chip, for example, via a wire connection between anelectrical lead and the laser diode chip.

In accordance with a further embodiment, the laser diode chip is basedon a nitride compound semiconductor material. The laser diode chip canhave, in particular, a substrate, preferably an electrically conductingsubstrate, for example, crystalline (In,Al,Ga)N. Thereabove it ispossible to apply an epitaxial layer sequence, that is to sayepitaxially grown semiconductor layers, which is based on a nitridecompound semiconductor material and is thus embodied on the basis ofInAlGaN.

Designations such as “InAlGaN-based compound semiconductor materials”,“(In,Al,Ga)N-based compound semiconductor materials” and “nitridecompound semiconductor materials” include, in particular, thosesemiconductor materials which comprise a material from the III-Vcompound semiconductor material system In_(x)Al_(y)Ga_(1-x-y)N where0≦x≦1, 0≦y≦1 and x+y≦1, that is to say, for example, GaN, AlN, AlGaN,InGaN, AlInGaN. The laser diode chip can have, in particular, on thesubstrate a semiconductor layer sequence having an active layer,particularly preferably on the basis of AlGaInN and/or InGaN, which isprovided for emitting light during operation. In particular, the laserdiode chip can emit light from an ultraviolet to green wavelength rangeduring operation.

In accordance with a further embodiment, the laser diode chip hassemiconductor layers on the substrate, said semiconductor layers having,for example, the active layer between waveguide layers and claddinglayers. In particular, it is possible to apply on the substrate a firstcladding layer, thereabove a first waveguide layer, thereabove theactive layer, thereabove a second waveguide layer and above the latter asecond cladding layer. Above the second cladding layer, it isfurthermore possible to arrange a semiconductor contact layer and, abovethe latter, an electrical connection layer, for example, in the form ofa metal layer. Electrical contact can be made with the laser diode chipparticularly preferably via the electrical connection layer situatedopposite the substrate and also via the conductive substrate, whereinthe substrate can also have an electrical connection layer on the sidefacing away from the semiconductor layers. In this case, the laser diodechip can thus be mounted on the mounting part by means of the solderlayer directly with the substrate or with an electrical connection layerof the laser diode chip, which layer is arranged on the side of thesubstrate facing away from the semiconductor layers. On that side of theactive layer which faces away from the substrate, a charge carrierbarrier layer can furthermore be arranged between the waveguide layerand the cladding layer in order to avoid a so-called charge carrierovershoot.

By way of example, the semiconductor layers arranged between thesubstrate and the active layer can be n-doped and the semiconductorlayers arranged above the active layer as seen from the substrate can bep-doped. As an alternative thereto, it is also possible to reverse thedoping order. The active layer can be undoped or n-doped. The laserdiode chip can have as active layer, for example, a conventional pnjunction, a double heterostructure or a quantum well structure,particularly preferably a multi quantum well structure (MQW structure).In the context of this application, the designation quantum wellstructure encompasses, in particular, any structure in which chargecarriers can experience a quantization of their energy states as aresult of confinement. In particular, a quantum well structure can havequantum wells, quantum wires and/or quantum dots and a combination ofthese structures. By way of example, the active layer can haveInGaN-based quantum films between suitably embodied barrier layers.

In accordance with one particularly preferred embodiment, for producingthe laser diode chip, as described above, firstly n-doped layers, thenthe active region and thereabove a p-doped layer are grown.

In accordance with a further particularly preferred embodiment, thelaser diode chip is arranged with the substrate on the mounting part,such that the laser diode chip has the preferably epitaxially depositedsemiconductor layers on that side of the substrate which faces away fromthe mounting part and the solder layer. This preferred mountingdirection is also designated hereinafter as “Epi up”.

In accordance with a further embodiment, the laser diode chip has aradiation coupling-out area with a radiation coupling-out region, viawhich the light generated in the active layer is emitted duringoperation. The radiation coupling-out region is typically defined by oneon the basis of internal waveguiding effects and a current densitydistribution chosen in a targeted manner on the radiation coupling-outarea. In this case, the laser diode chip is preferably embodied as anedge emitting laser diode chip, in which the radiation coupling-out areacan be produced, for example, by breaking, cleaving and/or etching asemiconductor layer composite assemblage along a crystal plane.Furthermore, the laser diode chip has a rear side area arranged oppositethe radiation coupling-out area. The radiation coupling-out area and therear side area are usually also designated as so-called facets in thecase of edge emitting laser diode chips. Furthermore, the laser diodechip has side areas which connect the rear side area and the radiationcoupling-out areas to one another and which are formed by the sides ofthe semiconductor layers which delimit the latter in a directionperpendicular to the growth and arrangement direction of thesemiconductor layers.

Here and hereinafter, the outer area of the laser diode chip which facesthe mounting part and is in direct contact with the solder layer is alsodesignated as underside, while the outer area situated opposite themounting part in the layer arrangement direction is designated as topside.

In accordance with a further embodiment, the laser diode chip isarranged directly on the mounting part by means of the solder layer andis thus mounted directly on the mounting part. That means, inparticular, that only the solder layer is arranged between the laserdiode chip and the mounting part. The solder layer has a thickness ofgreater than or equal to 3 μm. Particularly preferably, the thickness ofthe solder layer can also be greater than or equal to 4 μm andfurthermore also greater than or equal to 5 μm.

In accordance with a further embodiment, the solder layer comprises asoft solder and is preferably composed of a soft solder. In particular,the soft solder can be formed from an alloy comprising one or aplurality of metals selected from Sn, In and Au, for example,

-   -   AuSn, particularly preferably comprising 80% Au and 20% Sn,    -   AuGe, particularly preferably comprising 88% Au and 12% Ge,    -   SnPb, particularly preferably comprising 63% Sn and 37% Pb,    -   SnAg, particularly preferably comprising 96.5% Sn and 3.5% Ag or        95% Sn and 5% Ag or 80% Sn and 20% Ag,    -   SnPbAg, particularly preferably comprising 63% Sn, 35.6% Pb and        1.4% Ag,    -   SnIn, particularly preferably comprising 95% Sn and 5% In,    -   InAg, particularly preferably comprising 90% In and 10% Ag,    -   SnInAg, particularly preferably comprising 77% Sn, 21.2% In and        2.8% Ag,    -   SnCu, particularly preferably comprising 99% Sn and 1% Cu or        99.3% Sn and 0.7% Cu,    -   SnAgCu, particularly preferably comprising 95.5% Sn, 3.8% Ag and        0.7% Cu,    -   SnSb, particularly preferably comprising 95% Sn and 5% Sb,    -   SnAgSb, particularly preferably comprising 65% Sn, 25% Ag and        10% Sb,    -   SnBi, particularly preferably comprising 58% Bi and 42% Sn,    -   SnBiCu, particularly preferably comprising 90% Sn, 9.5% Bi and        0.5% Cu or 95% Sn, 3.5% Bi and 1.5% Cu or 95% Sn, 3% Bi and 2%        Cu,    -   SnBiInAg, particularly preferably comprising 78% Sn, 10% Bi, 10%        In and 2% Ag.

In accordance with one particularly preferred embodiment, the laserdiode device comprises a housing with a mounting part, on which a laserdiode chip based on a nitride compound semiconductor material is mountedin the housing directly by means of a solder layer and the solder layerhas a thickness of greater than or equal to 3 μm.

The fact that the laser diode chip is mounted directly on the mountingpart of the housing by means of the solder layer means, in particular,that, in the case of the laser diode device described here, noadditional heat sink such as is customary in the prior art is arrangedbetween the laser diode chip and the housing, which heat sink mightfunction as a heat spreader. Such a manner of mounting laser diode chipsin which an additional heat sink is used between the laser diode chipand the housing corresponds to the prior art. The additional heat sinkbelow the laser diode chip is usually a mounting body having goodthermal conductivity for the purpose of heat spreading and having athickness of more than 10 μm and typically, for example, 50 to 120 μm.This manner of mounting was optimized in particular for infrared and redlasers, particularly those based on arsenides, and heretofore has beentransferred to the mounting of nitride-based laser diode chips withoutsignificant modifications. In the case of the laser diode devicedescribed here, the contribution of the heat sink to the total thermalresistance is thus omitted. A 200 μm thick AlN heat sink, such as islikewise typically used in the prior art, has a thermal resistance ofapproximately 3 to 4 K/W.

In the case of infrared and red lasers which are based on arsenidiccompound semiconductor materials and are usually mounted “Epi down”owing to their substrate having poor thermal conductivity, if anadditional heat sink were dispensed with there would be a high risk ofthe active region being short-circuited by solder at the chip edges, orelse of solder migrating at the chip edges during operation andproducing such short circuits. Moreover dispensing with the heat sinkwould give rise to high strains and crystal defects in the laser diodechip during operation, so-called “dark line defects”, which arise duringcooling after soldering on account of the different coefficients ofthermal expansion of the chip and of the housing and which can lead tothe failure of the component. Although this risk can be reduced somewhatby the use of very soft solders, it is still too high. Soft solders suchas In furthermore tend toward migration and can thereby easily bringabout short circuits above the active region of a laser diode chip.

The inventors have recognized that, contrary to the previous assumptionsand procedures, such problems do not apply to laser diode chips based ona nitride compound semiconductor material. By way of example, it ispossible to use substrates having a thermal conductivity ofapproximately 200 W/mK instead of 46 W/mK in the case of GaAssubstrates. As a result, laser diode chips based on nitride compoundsemiconductor material can also be mounted “Epi up”, such that there isno increased risk of short circuits in the case of a preferred substratethickness of greater than or equal to 50 μm and less than or equal to150 μm, preferably, for example, a thickness of approximately 110 μm.“Dark line defects” are not known for nitride-based laser diode chipsand therefore likewise do not constitute a problem.

For a high quality of the mounting of the laser diode chip on themounting part of the housing without an additional heat sinktherebetween, the solder layer described here having a thickness ofgreater than or equal to 3 μm is particularly advantageous, while asolder layer that is as thin as possible is preferred for thermalreasons in the prior art. In particular, a soft solder described aboveis suitable for compensating for thermal strains during cooling afterthe soldering of the laser diode chip and for unevennesses of themounting part. Such unevennesses may be virtually unavoidable, forexample, if a mounting part based on copper with a steel sheathing isused. The use of the thick solder layer described here thus affordsthermal advantages in total since a soldering that is homogeneous and inparticular free of shrink holes, such as is possible by virtue of thethickness of the solder layer as described here, outweighs theinherently greater thermal resistance caused by the thickness of thesolder layer as described here in comparison with a thin solder layer.In particular, even though the heat sink that is usually used in theprior art is omitted, it is possible overall to achieve a reduction ofthe thermal resistance between the laser diode chip and the housing,wherein, for thermally linking the laser diode chip to the thick solderlayer as continuously as possible and over the largest possible area,the anchoring elements described further below can furthermoreparticularly preferably be provided in the laser diode chip. In the caseof the laser diode device described here, heat spreading can also beeffected in this case by means of the housing and in particular themounting part.

In particular, for the laser diode device described here, a significantincrease in the output power, in comparison with the prior art, to morethan 3 W is possible. However, such an increase is possible only throughthe combination of a housing having the best possible thermalconductivity, such as a copper-based housing, for example, with thethick solder layer, since, by way of example, although just the use ofsuch a thermally optimized housing can decrease the thermal resistanceby approximately 2 to 3 K/W, this is insufficient for achieving anoutput power of more than 3 W.

Externally, however, the laser diode device described here canadvantageously correspond totally to the components produced heretoforeaccording to the prior art and it can be produced with comparableprocesses suitable for mass production. The costs, measured for instancein dollars per watt, can thus be significantly reduced. Furthermore,fewer components are necessary for an identical light power in anapplication with the use of the laser diode device described here incomparison with known laser diodes.

In the case of customary laser diodes in which laser diode chips aremounted on a housing via an additional heat sink, the heat sink is ablenot only to act as a heat spreader but also to reduce strains which acton the chip, since the housing usually has a coefficient of thermalexpansion that is far above the coefficient of thermal expansion of thechip. Such compensation of strain by means of an additional heat sink isnot possible in the case of the laser diode device described here. Ifthe coefficients of thermal expansion differ excessively between thelaser diode chip and the housing, it can happen during cooling to roomtemperature after the soldering of the laser diode chip that the housingcontracts to a greater extent than the laser diode chip. As a result, itcan happen that the laser diode chip forms a convex curvature facingaway from the housing. As a result, chip shearing can occur, as a resultof which the laser diode chip is no longer soldered on optimally andover the whole area. Particularly preferably, therefore, the laser diodechip has a strain that endeavors to convexly deform the underside of thelaser diode chip facing the mounting part, or that counteracts at leasta concave deformation of the underside of the laser diode chip facingthe mounting part. By way of example, the laser diode chip can beembodied in such a way that, in an unmounted state, it has a bowl-shapedcurvature or at least a minimal bowl shape with a virtually planarembodiment. A suitable strain of the laser diode chip can be set, forexample, by means of growth conditions chosen in a targeted mannerduring the growth of the semiconductor layers on the substrate.

In accordance with a further embodiment, the laser diode chip has, inthe underside facing the mounting part, at least one anchoring elementfor the solder of the solder layer. The anchoring element can be formed,for example, by a depression or an elevation in the underside of thelaser diode chip facing the mounting part. Preferably, the laser diodechip has a plurality of anchoring elements, which can be shaped and/orarranged regularly or irregularly. One or a plurality of anchoringelements can, for example, also be formed in a manner adjoining sideareas of the laser diode chip, that is to say at chip edges between theunderside of the laser diode chip facing the solder layer and theradiation coupling-out area and/or the rear side area and/or one or aplurality of side areas, in each case as a stepped depression. By meansof the anchoring elements, it is possible to achieve an interlinking ofthe solder and of the laser diode chip which can counteract chipshearing in addition or as an alternative to an above-described targetedstrain of the laser diode chip. In the preferred “Epi up” mountingdescribed above, the at least one and preferably the plurality ofanchoring elements are formed in the substrate.

The at least one and preferably the plurality of anchoring elements canbe introduced, for example, in a targeted manner as discrete elevationsor depressions. The anchoring elements can have, in particular,punctiform elevations and/or depressions or else linear elevationsand/or depressions. By way of example, anchoring elements can also beformed by a targeted roughening or a targeted mechanical or chemicalremoval. Furthermore, it is also possible for an anchoring element to beprovided, for example, in the form of a step in the region of thesubstrate edge at one or both facets, that is to say the radiationcoupling-out area and/or the rear side area.

In order to produce the at least one anchoring element and preferablythe plurality of anchoring elements, it is possible preferably to carryout dry- or wet-chemical etching, in particular anisotropic etchingmethods, lithographic patternings and/or mechanical patternings.

Preferably, the at least one and preferably the plurality of anchoringelements has a depth of greater than or equal to 0.1 μm and less than orequal to 10 μm and preferably of greater than or equal to 0.5 μm andless than or equal to 5 μm. A size of greater than or equal to 0.1 μmand preferably greater than or equal to 0.5 μm is particularly suitablesuch that a sufficient interlinking between the laser diode chip and thesolder arises, while a depth of less than or equal to 10 μm andpreferably of less than or equal to 5 μm is particularly suitable forachieving a complete filling or enclosing of an anchoring element withthe solder and thus a linking of the laser diode chip to the solderlayer over the largest possible area.

In accordance with a further embodiment, the laser diode chip has ametallization on the side areas and/or the radiation coupling-out areaand/or the rear side area. The metallization can be embodied, inparticular, in the form of a metal layer. The metallization is thusembodied in particular in a layered fashion with a main extension planethat is parallel to the arrangement direction of the semiconductor layersequences of the laser diode chip. By means of such a metallization, acooling of the laser diode chip can be achieved via the areas of thelaser diode chip that are provided with the metallization. By way ofexample, the metallization can be arranged directly on the substrate andat least some semiconductor layers. Particularly preferably, themetallization is in this case arranged, as seen from the mounting part,below the active layer, that is to say—in the case of “Epi up” mountingdescribed above—on side areas of the substrate and side areas of thosesemiconductor layers which are arranged between the substrate and theactive layer. This makes it possible to prevent the metallization fromcausing a short circuit by a bridging of the n- and p-doped layers aboveand below the active layer. Effective heat dissipation can be madepossible on account of such a direct contact of the metallization withthe semiconductor material of the laser diode chip.

If the metallization is arranged on the radiation coupling-out areaand/or the rear side area directly in contact with the semiconductorlayers, then the metallization is preferably situated between thesemiconductor layers and an optical layer on the radiation coupling-outarea and/or the rear side area. The optical layer is formed, inparticular, by the facet reflective coating or antireflective coatingthat is customary for laser diode chips. Usually, the optical layer onthe radiation coupling-out area and the rear side area is formed from adielectric material or a dielectric layer sequence. If a metallizationis provided on the radiation coupling-out area, then the radiationcoupling-out region remains free of the metallization, such that thelight generated in the active layer can be emitted without beingimpeded.

Furthermore, it is also possible for a metallization to form an outerside of the laser diode chip. In other words, the metallization is notcovered by a further layer of the laser diode chip. In the case wherethe metallization is arranged on the side areas, the metallization canboth be applied directly on the semiconductor layers and form outersides of the laser diode chip. If the metallization is arranged on theradiation coupling-out area and/or the rear side area and forms an outerside of the laser diode chip, then this means, in other words, that themetallization is arranged on the optical layer of the radiationcoupling-out area or the rear side area. In particular, themetallization can extend as far as the underside of the laser diodechip. What can be achieved by means of a metallization that forms anouter side of the laser diode chip is that the solder of the solderlayer can wet the metallization. As a result, a part of the solder layercan “run up” to the metallization in a targeted manner and thus makepossible a good thermal contact and hence a good heat dissipation of thelaser diode chip via the areas of the laser diode chip that are providedwith the metallization.

The metallization can comprise, in particular, one or more of the metalsAu, Ti, Pt, Cr, Pd, Ni, Ag, W, Cu.

In accordance with a further embodiment, the laser diode chip has, on atop side facing away from the mounting part, at least one depressionwhich extends from the rear side area to the radiation coupling-out areaand which is covered with a passivation. In particular, the depressionprojects into the semiconductor layer sequences to above the activelayer as seen from the top side. Preferably, the laser diode chip hastwo depressions which in each case extend from the radiationcoupling-out area to the rear side area and between which a contactregion is arranged on the top side, via which contact region a targetedcurrent impression or current density distribution in the laser diodechip, and in particular in the active layer, is produced. Consequently,the depressions with the passivation are preferably situated betweenpossible migration paths of the solder along which the solder could movefrom a metallization on the side areas of the laser diode chip towardthe contact region. It is thereby possible to prevent the solder fromrunning up in an uncontrolled manner at the chip edges, or to prevent anuncontrolled migration of solder in the region of the laser diodedevice, which would cause a short-circuiting of the active layer. Thedepressions can also be designated as so-called mesa trenches thatinterrupt the active layer.

Since, in comparison with laser diodes in the prior art, a significantreduction of the thermal resistance can be achieved by means of theconfiguration of the laser diode device as described here, it ispossible to operate laser diode chips with a larger active area, that isto say a larger energized area, in comparison with the prior art. In thelaser diode device described here, therefore, it is possible to uselaser diode chips having a longer and/or wider energized area incomparison with the prior art. In particular, the active layer can havean area of greater than or equal to 2500 μm², preferably of greater thanor equal to 10 000 μm² and particularly preferably of greater than orequal to 20 000 μm² up to 30 000 μm². In this case, a decrease in thecurrent density from a maximum value to 10% is assumed as areadelimitation.

Furthermore, in the case of the laser diode device described here, it isalso possible, unlike in the prior art, without further outlay, to usemore than one laser diode chip in one of the housings described here,whereby an increase in the output power can likewise be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, advantageous embodiments and developments willbecome apparent from the exemplary embodiments described below inconjunction with the figures.

In the figures:

FIGS. 1A and 1B show schematic illustrations of a laser diode device inaccordance with an exemplary embodiment,

FIG. 2 shows a schematic illustration of a laser diode chip inaccordance with a further exemplary embodiment,

FIG. 3 shows an excerpt from a laser diode device in accordance with afurther exemplary embodiment,

FIGS. 4A to 4C show excerpts from laser diode devices in accordance withfurther exemplary embodiments, and

FIGS. 5A to 11 show schematic illustrations of excerpts from laser diodedevices in accordance with further exemplary embodiments.

In the exemplary embodiments and figures, elements that are identical,of identical type or act identically may in each case be provided withthe same reference signs. The illustrated elements and their sizerelationships among one another should not be regarded as true to scale;rather, individual elements such as, for example, layers, structuralparts, components and regions may be illustrated with an exaggeratedsize in order to enable better illustration and/or in order to afford abetter understanding.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIGS. 1A and 1B show an exemplary embodiment of a laser diode device100, wherein FIG. 1A shows a schematic sectional illustration and FIG.1B a plan view of the laser diode device 100. The following descriptionrelates equally to FIGS. 1A and 1B.

The laser diode device 100 comprises a housing 1, in which a laser diodechip 2 is mounted on a mounting part 11 by means of a solder layer 3.

The housing 1 has the highest possible thermal conductivity and isembodied in the form of a so-called TO housing in the exemplaryembodiment shown. In this case, the housing 1 has a housing part 10 andthe mounting part 11 arranged at the housing part. The mounting part 11extends away from the housing part 10 and is embodied integrally withthe housing part 10 in the exemplary embodiment shown. For this purpose,the housing part 10 and the mounting part 11 have a main body formedfrom a metal, which is copper in the exemplary embodiment shown.

The housing part 10 furthermore has a sheathing 12 composed of steel,which is formed by a coating of the copper main body in the region ofthe housing part 10. The mounting part 11 can be formed by an uncoatedmain body, that is to say by the copper main body in the exemplaryembodiment shown, or, as is indicated by the dashed line around themounting part 11, can likewise have a sheathing, preferably a steelsheathing.

Furthermore, the housing part 10 can have holes or openings, forexample, in which are arranged small lead legs projecting from that sideof the housing part 10 which faces away from the mounting part 11 to theside of the mounting part 11. Small lead legs arranged and fixed thereincan be embodied as electrical feedthroughs, for example, and affordpossibilities for electrical contact-making.

A housing cover 14 is preferably arranged above the mounting part 11 andthus above the laser diode chip 2, as is indicated by the dashed lines.The housing cover 14, which can furthermore have a window 15, cancomprise steel, for example, and preferably be composed of steel, apartfrom the window 15. By virtue of the fact that the housing part 10 hasthe steel sheathing 12 in the exemplary embodiment shown here, thehousing cover 14 can be applied on the housing part 10 of the housing 1and, as in customary TO housings having steel bases, can be fixed bymeans of welding in a standard process.

As an alternative to the housing 1 of TO design shown here, the housing1 can also be embodied differently therefrom. By way of example, thehousing 1 can have a mounting part 11 composed of ceramic or a metal, onwhich a housing cover is arranged directly or on additional side parts.Furthermore, the mounting part 11 can, for example, also be formed by ametal-core circuit board. Independently of the geometrical andmaterial-specific configuration of the housing 1, the latter preferablyhas the highest possible thermal conductivity.

The mounting part 11 has a mounting area 13, on which a laser diode chip2 is arranged. In particular, the laser diode chip 2 is mounted directlyon the mounting area 13 of the mounting part 11 by means of the solderlayer 3 and is thereby electrically and thermally connected to thehousing 1. Consequently, only the solder layer 3 is arranged between thelaser diode chip 2 and the mounting part 11.

The solder layer 3 has a thickness of greater than or equal to 3 μm andis formed by a soft solder, in particular a soft solder based on one ora plurality of metals selected from Sn, In and Au. In particular, thesolder layer can be formed by one of the solder materials mentionedabove in the general part.

While it is customary for the purpose of optimum heat dissipation instandard laser diode components to couple a laser diode chip to ahousing via a solder layer that is as thin as possible, in order toobtain a thermal resistance that is as low as possible, the solder layer3 of the laser diode 100 described here has a thickness of greater thanor equal to 3 μm. The thickness of the first solder layer 3 can also begreater than or equal to 4 μm or even greater than or equal to 5 μm. Itis thereby possible to compensate for thermally induced stresses thatoccur during operation as a result of the heat generated in the laserchip 2 or the cooling effected after the soldering of the laser diodechip 2 and the different coefficients of thermal expansion of the laserdiode chip 2 and of the housing 1. Furthermore, by way of example,surface unevennesses on the mounting area 13 of the mounting part 11 canalso be compensated for by such a thick solder layer. Said unevennessescan occur in particular when the mounting part 11 has the copper mainbody shown here and a sheathing composed of steel.

Preferably, as is shown in FIG. 2 in accordance with one preferredexemplary embodiment, the laser diode chip 2 is embodied as an edgeemitting laser diode chip having a radiation coupling-out area 27 formedby a side area and a rear side area 28 situated opposite the radiationcoupling-out area. The radiation coupling-out area 27 has a radiationcoupling-out region 270, via which the laser radiation generated in thelaser diode chip 2 is emitted during operation. Furthermore, the laserdiode chip 2 has side areas which connect the radiation coupling-outarea 27 and the rear side area 28 to one another. Preferably, on theradiation coupling-out area 27 and the rear side area 28 there areapplied optical layers (not shown) which form reflective and/orantireflective layers and by means of which a resonator having thedesired reflection and coupling-out properties is formed.

In particular, the laser diode chip 2 is based on a nitride compoundsemiconductor material. For this purpose, the laser diode chip 2 has asubstrate 20, which is preferably embodied as electrically conductingand, for example, comprises crystalline (In,Al,Ga)N or is composedthereof. A semiconductor layer sequence based on a nitride compoundsemiconductor material is grown thereabove, preferably by means of anepitaxy method such as, for example, metal organic vapor phase epitaxy(MOVPE). The laser diode chip 2 has, on the substrate 20, an activelayer 23 arranged between waveguide layers 22 and cladding layers 21. Inparticular, the laser diode chip 2 has a first cladding layer 21 on thesubstrate 20, on which first cladding layer a first waveguide layer 22and thereabove the active layer 23 are arranged. Above the active layer23 there follow in the growth direction a further waveguide layer 22 andalso a further cladding layer 21 and thereabove a semiconductor contactlayer 24, with which contact is made by an electrical connection layer25, for example, in the form of a metallic electrode layer. The laserdiode chip 2 is electrically connected via the electrical connectionlayer 25 and the electrically conducting substrate 20, which can have afurther electrical connection layer (not shown) on the side facing awayfrom the semiconductor layers 21, 22, 23 and 24. The electricalconnection layer 25 can be in electrical contact only with a partialregion of the semiconductor contact layer 24, for example, by means of apatterning, in order to achieve a current impression into a region ofthe active layer 23 chosen in a targeted manner.

The arrangement direction of the laser diode chip 2 with the substrate20 directly on the solder layer 3 as shown is also designated as “Epiup”.

In the exemplary embodiment shown, as seen from the active layer 23, thesemiconductor layers facing the substrate 20 are n-doped, while thesemiconductor layers designated by the reference sign 26 and arranged onthat side of the active layer 23 which faces away from the substrate 20are p-doped. The active layer 23 can be n-doped or undoped, for example,and can have a multi quantum well structure, in particular, in theexemplary embodiment shown.

Hereinafter, that side of the laser diode chip 2 which is situatedopposite the solder layer 3 is designated as the top side 30, and thatside of the laser diode chip 2 which faces the solder layer 3 and isdirectly in contact with the solder layer 3 is designated as theunderside 31. The top side can be formed, for example, at least partlyby the electrical connection layer 25. If the electrical connectionlayer 25 is embodied in a patterned fashion, the top side 30 can also beformed partly by an exposed partial region of the semiconductor contactlayer 24 and/or, for example, by a passivation layer applied in partialregions on the electrical connection layer 25 and/or the semiconductorcontact layer 24.

The material of the mounting part 11, which, as described above, can beformed, for example, by the copper main body or some other materialhaving a high thermal conductivity, usually has a significantly highercoefficient of thermal expansion than the laser diode chip 2. As aresult, in particular after the laser diode chip 2 has been solderedonto the mounting part 11 of the housing 1, strains can occur betweenthe laser diode chip 2 and the mounting part 11, which, depending on thechoice of solder, can possibly be compensated for only in part by meansof the solder layer 3. As a consequence thereof, it could happen that,during cooling after the soldering of the laser diode chip 2, themounting part 11 contracts to an extent such that the laser diode chip 2on the solder layer 3 is curved up and has a convex bend on the top side30 facing away from the mounting part 11. Accordingly, the underside 31of the laser diode chip 2 facing the mounting part 11 is shapedconcavely in this case. The contraction of the mounting part 11 duringcooling is indicated by the dashed arrows. If the curvature of the laserdiode chip 2 is too great, at least partial chip shearing can occur,that is to say an at least partial detachment of the laser diode chip 2from the solder layer 3. Particularly preferably, therefore as indicatedby the dotted line in FIG. 3, the laser diode chip 2 has a strain whichendeavors to convexly deform the underside 31 of the laser diode chip 2facing the mounting part 11 in an unmounted state. In other words, thelaser diode chip 2 can be produced such that after production itpreferably has the bowl-shaped curvature indicated by the dotted line inFIG. 3. The laser diode chip 2 can also be embodied such that it isstill slightly bowl-shaped after the cooling of the solder of the solderlayer 3. As an alternative thereto, the laser diode chip 2 can also beembodied in a planar fashion or in a virtually planar fashion with aminimal bowl shape and nevertheless have a strain in the semiconductorlayers which is suitable for at least partly compensating for thethermal strains that can occur during cooling after the solderingprocess and which at least partly counteracts a concave deformation ofthe underside 31 of the laser diode chip 2 facing the mounting part 11.

A corresponding strain of the semiconductor layers of the laser diodechip 2 can be set by means of suitably chosen process parameters duringthe growth of the semiconductor layers.

As an alternative or in addition to the strain indicated in FIG. 3, thelaser diode chip 2 can also have on the underside 31 at least oneanchoring element 32 and preferably a plurality of anchoring elements 32formed by depressions and/or elevations. FIGS. 4A to 4C show examples ofsuch anchoring elements 32, which in particular can also be present incombinations. A sufficient adhesion of the laser diode chip 2 to thesolder layer 3 can be achieved by means of the anchoring elements 32,whereby a large-area thermal connection and, as a result, a reduction ofthe thermal resistance between the laser diode chip 2 and the housing 1can be achieved.

In FIG. 4A, the anchoring element 32 is formed by a depression at thechip edge between the radiation coupling-out area 27 and the underside31, into which the solder of the solder layer 3 can engage. Such ananchoring element 32, which is embodied as a depression and whichpreferably extends along the chip edge and is embedded in a steppedfashion, can be introduced in a targeted manner in order to achieve aninterlinking of the chip edge with the solder of the solder layer 3.Alternatively or additionally, an anchoring element 32 embodied as astepped depression can also be provided at a chip edge between theunderside 31 and the rear side area 28 and/or the underside 31 and aside area 29. Furthermore, a respective anchoring element 32 embodied asa stepped depression can be provided at all chip edges at the underside31.

FIGS. 4B and 4C show, as anchoring element 32, a depression and anelevation in the underside 31 of the laser diode chip 2. These can beproduced by means of a targeted patterning of the underside 31 of thelaser diode chip and, for example, can also be embodied in a pluralityregularly as discrete punctiform or linear elevations or depressions.Preferably, a multiplicity of anchoring elements 32 in the form ofelevations and depressions can also be produced by means of a rougheningof the underside 31. In this case, the anchoring elements 32 arearranged in a manner distributed stochastically over the entireunderside 31 and can merge into one another.

The anchoring elements 32 in accordance with the exemplary embodimentsshown can be produced, for example, by dry- or wet-chemical etching, inparticular anisotropic etching, lithographic patterning and/ormechanical patterning.

The anchoring elements 32 preferably have a size, that is to say a widthand/or a depth or height, such that the solder of the solder layer 3 canpenetrate into or between the anchoring elements 32. Preferably, forthis purpose, the size of the anchoring elements is greater than orequal to 0.1 μm and particularly preferably greater than or equal to 0.5μm. Furthermore, the anchoring elements 32 have a size which ismaximally of a magnitude such that the solder of the solder layer 3 cancompletely mold around or fill said anchoring elements, such that thesolder layer 3 and the underside 31 of the laser diode chip 2 can belinked in a manner free of shrink holes and blisters. For this purpose,the anchoring elements preferably have a size of less than or equal to10 μm and preferably of less than or equal to 5 μm.

FIGS. 5A to 11 show excerpts from further exemplary embodiments, whichcan be combined with the abovementioned exemplary embodiments and inwhich the laser diode chip 2 has a metallization 6 on at least one sidearea 29, the radiation coupling-out area 27 and/or the rear side area28. The metallization 6 is formed by one or a plurality of metal layerswhich preferably comprise or are composed of Au, Ti, Pt, Cr, Pd, Ni, Ag,W, Cu or mixtures or alloys thereof. By means of the metallization, theareas of the laser diode chip 2 which are coated thereby can beadditionally cooled, as a result of which more effective heatdissipation can be made possible.

Optical layers 7 in the form of reflective or antireflective layers areshown on the facets, that is to say on the radiation coupling-out area27 and the rear side area 28, of the laser diode chip 2 described below.

FIGS. 5A and 5B show, in a plan view of the top side and in a sectionalillustration parallel to the radiation coupling-out area 27, a laserdiode chip 2 having a respective metallization 6 on the side areas 29which connect the radiation coupling-out area 27 and the rear side area28 to one another. In this case, the metallization 6 is arranged indirect contact with the substrate and the semiconductor layers of thelaser diode chip 2 and simultaneously forms outer areas of the laserdiode chip 2. As is evident from FIG. 5B, the metallization 6 isarranged below the active layer 23 as seen from the mounting part 11 orfrom the underside 31, in order to avoid a short-circuiting of the n-and p-doped sides of the laser diode chip 2. By virtue of the fact thatthe metallizations 6 form outer sides of the laser diode chip 2, thesolder of the solder layer 3 can wet them and climb up them, as isindicated in FIG. 5B. It is thereby possible to achieve a good thermalcontact between the side areas 29 of the laser diode chip 2 and thesolder layer 3, whereby the side areas 29 can contribute to the heatdissipation of the laser diode chip 2.

FIGS. 6 and 7 show excerpts from further exemplary embodiments, inwhich, as in the exemplary embodiment in FIGS. 5A and 5B, metallizations6 are arranged on the side areas 29. In the case of such an arrangementof the metallization on the side areas, there is an increased risk ofshort circuits at the side edges, which risk can be caused by theapplied metallization 6 and/or by the solder climbing up during thesoldering process, since metal particles can migrate to the active layer23 and, for example, bridge the latter. The laser diode chips 2 in theexemplary embodiments in FIGS. 6 and 7 therefore have depressions 33,which preferably extend from the radiation coupling-out area 27 as faras the rear side area 28 and which are covered with a passivation 34,for example, a dielectric oxide such as SiO₂, for instance. Thedepressions 33 have a depth such that, as seen from the top side 30,they reach as far as below the active layer 23. It is thereby possibleto achieve a barrier for solder particles or particles of themetallizations 6, such that these can no longer lead to a short circuit.

As is shown in FIG. 6, the depressions 33 can be formed at the chipedges between the top side 30 and the side areas 29. Furthermore, as isshown in FIG. 7, the depressions 33 can also be drawn further inward inthe direction of the energized region of the active layer 23, saidregion being defined by a patterned electrical connection layer 25. Thedepressions 33 can also be designated as mesa trenches.

FIG. 8 shows a further exemplary embodiment, in which metallizations 6are arranged on the optical layers 7 on the radiation coupling-out area27 and the rear side area 28 and form outer sides of the laser diodechip 2, as a result of which solder of the solder layer 3 can climb upthe radiation coupling-out area 27 and the rear side area 28 and canthus lead to a good thermal connection of the facets of the laser diodechip 2 to the solder layer 3 and thus to the housing 1. Particularly inthe case of a metallization 6 on the radiation coupling-out area 27, itis important for the metallization 6, as shown in FIG. 8, to be arrangedbelow the active layer 23 as seen from the underside 31, such that theradiation coupling-out region 270 is free of the metallization 6.

FIG. 9 shows a plan view of a further exemplary embodiment of a laserdiode chip 2, in which both the radiation coupling-out area 27, the rearside area 28 and the side areas 29 are provided with a metallization 6,such that the laser diode chip 2 can be thermally connected all around.

FIG. 10 shows a further exemplary embodiment of a laser diode chip 2, inwhich, in comparison with the exemplary embodiment in FIG. 8, themetallization 6 is arranged directly on the radiation coupling-out area27 and the rear side area 28. In other words, the metallization 6 isarranged between the semiconductor layers of the laser diode chip 2 andthe optical layers 7 on the radiation coupling-out area and the rearside area 28. As a result, although wetting of the metallization 6 bythe solder of the solder layer 3 cannot be achieved, particularlyeffective heat dissipation of the facets of the laser diode chip 2 cannevertheless be achieved by virtue of the direct contact of themetallization 6 with the radiation coupling-out area 27 and the rearside area 28.

FIG. 11 shows a further exemplary embodiment of a laser diode chip 2, inwhich, in comparison with the previous exemplary embodiment, the opticallayers 7 are only partly applied on the radiation coupling-out area 27and the rear side area 28 and, in particular, do not reach as far as thesolder layer 3, such that a combination of the advantages of theexemplary embodiments in the previous figures can be achieved since themetallization 6 is arranged directly on the facets and at the same timecan be wetted by the solder of the solder layer 3.

The features described and shown in the figures and exemplaryembodiments can be combined with one another in accordance with furtherexemplary embodiments, even if such combinations are not explicitlyshown or described in the figures. Furthermore, the exemplaryembodiments shown in the figures can also have alternative or additionalfeatures in accordance with the embodiments in the general part.

The invention is not restricted to the exemplary embodiments by thedescription on the basis of said exemplary embodiments. Rather, theinvention encompasses any novel feature and also any combination offeatures, which in particular includes any combination of features inthe patent claims, even if this feature or this combination itself isnot explicitly specified in the patent claims or exemplary embodiments.

The invention claimed is:
 1. A laser diode device comprising: a housinghaving a mounting part; a laser diode chip based on a nitride compoundsemiconductor material in the housing on the mounting part, the chiphaving, on a substrate, semiconductor layers with an active layer forgenerating light and the chip having a radiation coupling-out area witha radiation coupling-out region for emitting the generated light, a rearside area situated opposite the radiation coupling-out area, and sideareas connecting the radiation coupling-out area and the rear side area;and a solder layer, wherein the laser diode chip is mounted directly onthe mounting part by means of the solder layer, wherein the solder layerhas a thickness of greater than or equal to 3 μm, and wherein thehousing has a housing part connected to the mounting part, the housingpart and the mounting part have a main body composed of copper, and atleast the housing part is steel-sheathed.
 2. The laser diode deviceaccording to claim 1, wherein the substrate is an electricallyconductive substrate composed of crystalline (In, Al, Ga)N and the laserdiode chip is mounted on the mounting part by means of the solder layerdirectly with the substrate or with an electrical connection layer ofthe laser diode chip, the electrical connection layer being arranged ona side of the substrate facing away from the semiconductor layers. 3.The laser diode device according to claim 1, wherein the mounting parthas a metal-core circuit board or a main body composed of metal orceramic.
 4. The laser diode device according to claim 1, wherein thehousing has a housing cover above the mounting part, the housing coverclosing the housing.
 5. The laser diode device according to claim 1,wherein the solder layer comprises a soft solder.
 6. The laser diodedevice according to claim 1, wherein the laser diode chip has a strainthat endeavors to convexly deform an underside of the laser diode chipfacing the mounting part, or that counteracts at least a concavedeformation of the underside facing the mounting part.
 7. The laserdiode device according to claim 1, wherein the laser diode chip has, inan underside facing the mounting part, at least one anchoring elementfor the solder layer, the at least one anchoring element being formed bya depression or elevation.
 8. The laser diode device according to claim7, wherein the laser diode chip has a plurality of anchoring elementsembodied as elevations and/or depressions in the underside.
 9. The laserdiode device according to claim 7, wherein the laser diode chip has asanchoring element a stepped depression at a chip edge between theunderside and the radiation coupling-out area or the rear side area or aside area.
 10. The laser diode device according to claim 1, wherein thelaser diode chip has a metallization on the side areas.
 11. The laserdiode device according to claim 1, wherein the laser diode chip has ametallization on the radiation coupling-out area and/or the rear sidearea.
 12. The laser diode device according to claim 11, wherein themetallization is arranged directly on the semiconductor layers betweenthe semiconductor layers and an optical layer on the radiationcoupling-out area and/or the rear side area.
 13. The laser diode deviceaccording to claim 10, wherein the metallization forms outer sides ofthe laser diode chip and a solder of the solder layer wets themetallization.
 14. The laser diode device according to claim 10, whereinthe metallization comprises at least one or more metals selected fromthe group consisting of Au, Ti, Pt, Cr, Pd, Ni, Ag, W and Cu.
 15. Thelaser diode device according to claim 10, wherein the laser diode chiphas, on a top side facing away from the mounting part, at least onedepression that extends from the rear side area to the radiationcoupling-out area and that is covered with a passivation.
 16. A laserdiode device comprising: a housing having a mounting part; a laser diodechip based on a nitride compound semiconductor material in the housingon the mounting part, the chip having, on a substrate, semiconductorlayers with an active layer for generating light and the chip having aradiation coupling-out area with a radiation coupling-out region foremitting the generated light, a rear side area situated opposite theradiation coupling-out area, and side areas connecting the radiationcoupling-out area and the rear side area; and a solder layer, whereinthe laser diode chip is mounted directly on the mounting part by meansof the solder layer, wherein the solder layer has a thickness of greaterthan or equal to 3 μm, and wherein the laser diode chip has a strainthat endeavors to convexly deform an underside of the laser diode chipfacing the mounting part, or that counteracts at least a concavedeformation of the underside facing the mounting part.
 17. A laser diodedevice comprising: a housing having a mounting part; a laser diode chipbased on a nitride compound semiconductor material in the housing on themounting part, the chip having, on a substrate, semiconductor layerswith an active layer for generating light and the chip having aradiation coupling-out area with a radiation coupling-out region foremitting the generated light, a rear side area situated opposite theradiation coupling-out area, and side areas connecting the radiationcoupling-out area and the rear side area; and a solder layer, whereinthe laser diode chip is mounted directly on the mounting part by meansof the solder layer, wherein the solder layer has a thickness of greaterthan or equal to 3 μm, and wherein the laser diode chip has, in anunderside facing the mounting part, at least one anchoring element forthe solder layer, the at least one anchoring element being formed by adepression or elevation.
 18. The laser diode device according to claim17, wherein the laser diode chip has a plurality of anchoring elementsembodied as elevations and/or depressions in the underside.
 19. Thelaser diode device according to claim 17, wherein the laser diode chiphas as anchoring element a stepped depression at a chip edge between theunderside and the radiation coupling-out area or the rear side area or aside area.
 20. A laser diode device comprising: a housing having amounting part; a laser diode chip based on a nitride compoundsemiconductor material in the housing on the mounting part, the chiphaving, on a substrate, semiconductor layers with an active layer forgenerating light and the chip having a radiation coupling-out area witha radiation coupling-out region for emitting the generated light, a rearside area situated opposite the radiation coupling-out area, and sideareas connecting the radiation coupling-out area and the rear side area;and a solder layer, wherein the laser diode chip is mounted directly onthe mounting part by means of the solder layer, wherein the solder layerhas a thickness of greater than or equal to 3 μm, wherein the laserdiode chip has a metallization on the side areas, and wherein the laserdiode chip has, on a top side facing away from the mounting part, atleast one depression that extends from the rear side area to theradiation coupling-out area and that is covered with a passivation.